It has long been known that grooved, rigid members such as wafers or blocks are useful for supporting and aligning optical fibers. For example, U.S. Pat. No. 3,864,018, issued to C. M. Miller on Feb. 4, 1975,describes silicon wafers having multiple, parallel, V-shaped grooves formed in their upper and lower surfaces by crystallographic etching. In this patent, block-like structures having arrayed, parallel channels are created by stacking the wafers such that upper-surface grooves meet corresponding lower-surface grooves. Multiple optical fibers are aligned and potted in the channels to create an alignment block. A face of the block can be sawed along a plane perpendicular to the fibers, and subsequently polished, to make a mass fiber end-connector.
More recently, practitioners have used members having V-grooves to align the end portions of optical fibers in optical fiber connectors that are simple enough for field installation. One general category of such connectors makes use of a block or base member having a V-groove in its upper surface, into which the fiber end-portions are placed, and clamps for pushing down on the fiber portions to hold them in the groove. However, those connectors that have been proposed are too imprecise to join single-mode fibers, or else are expensive to manufacture because they involve complicated parts, or expensive materials in significant quantities, or relatively inexpensive materials together with stringent manufacturing standards.
For example, S. Nagasawa and I. Sankawa, "Reliability of V-Groove Optical Fiber Mass Splicing-Improvement of Splice Loss Temperature Characteristics," Rev. Electr. Commun. Lab., (Japan), Vol. 33, No. 6 (1985), pp. 961-969, describes a connector comprising a plastic base and a pair of end blocks. Each fiber end-portion is engaged in one of the end blocks, and then the end blocks are mounted on the base such that the fiber end-portions are aligned and abutted in V-grooves on the base. Similarly, M. L. Dakss et al., "Field-Installable Connectors and Splice for Glass Optical Fiber Communications Systems," Twelfth Annual Connector Symposium Proceedings, Fort Worth, PA, Electronic Connector Study Group, Inc. (1979) pp. 197-206, also describes a plastic V-groove connector having three sections. Two plastic side pieces, each having a downward-sloping V-groove in its upper surface, engage a plastic central section by means of prongs and a locking screw. Two fiber ends meet in a V-groove in the upper surface of the central section. Such three-section connectors as the Nagasawa connector and the Dakss connector are disadvantageous in that they require the manufacture of three interlocking parts, and adequate precision can be assured in a plastic V-groove only by imposing stringent, and therefore relatively expensive, manufacturing standards.
As a further example, U.S. Pat. No. 4,784,456,issued to J. G. Smith on Nov. 15, 1988, and also M. -C. Soster et al., "New Low-Loss Mechanical Splices and the Special Tool Kit for Optical Communication," Rev. Tech. Thomson-CSF(France), Vol. 17, No. 3 (1985) pp. 617-629, each describe a plastic connector comprising a grooved bottom section hinged to three top sections. Each of the top sections includes a projection that, when the section is in its closed position, urges and locks a fiber into position in a V-groove in the bottom section. These connectors are disadvantageous because it is relatively expensive to manufacture the complicated parts that are required.
As yet a further example, U.S. Pat. No. 4,756,591 issued to K. Fischer et al., on Jul. 12, 1988, describes a connector comprising a silicon base member having a V-groove cut in its upper surface. The upper surface has two end portions, and a central portion in which the two fiber ends meet. To hold the fibers in place, an elastomeric layer is pressed down on each of the portions of the upper surface. The force on the elastomeric layer is provided, for example, by a spring. A particular kind of spring described by Fischer is a retaining spring installed within a U-shaped claw that slips axially over the end of the base member and engages longitudinal flutes in the sides of the base member. This connector is disadvantageous because silicon is a relatively expensive material from which to manufacture an entire base member, and as a consequence, the resulting connector is relatively expensive.
Thus, practitioners in the field have only been partially successful in the search for a field-installable optical connector that is simple to use, economical to manufacture, and that is able to align pairs of fibers with high precision.